Cross linking of fatty polyamides with ionizing radiation



3,098,806 CRGSS LENKING 9F FATTY PQLYAMIDES WITH KONIZHNG RADIATKON Raymond F. Paschke, Anoka, Minn, assignor to General Mills, End, a corporation of Delaware No Drawing. Filed Dec. 10, 1959, Ser. No. 858,583 Claims. (ill. 204-154) This invention relates to a method of cross linking and increasing the melting point of certain fatty acid polyamides by exposure to ionizing radiation and in particular to increasing the melting point of such polyamides which initially have low melting points.

Fatty polyamides are known to be useful in the field of casting, molding, adhesives and other well known applications. It has now been found that if such polyamides are subjected to ionizing radiation, cross linking occurs which results in raising the melting point of the polyamides. It has been found that great increases in the melting point can be accomplished with dosages of' gamma radiation. These polymerized products show improved properties such as greater strength and adhesion.

It is an object of this invention to increase the melting point of fatty polyamides by exposure to ionizing radiation.

It is also an object of this invention to cross link fatty acid polya-mides with ionizing radiation.

It is also an object of this invention to provide fatty acid polyamides having an increased melting point.

Briefly the invention consists of subjecting fatty acid polyamides to ionizing radiation such as gamma radiation so as to accomplish cross linking which results in raising the melting point.

The radiation used in this invention was Co gamma radiation. However, any other source of radiation can be used, such as spent atomic fuel rods. In addition electron accelerato-rs can be used as a means of cross linking the polyamides.

A variety of low melting point polyamides derived from higher fatty acids may be employed in this invention. By low melting point polyamides is meant those polyamides having a melting point below 130 C. In particular, the low melting point polyamides which have been found to be useful in this invention are those prepared from the amidic fatty acids, the epoxidized fatty acids and the polymeric fat acids. By fatty acid polyamide as used herein is meant (a) the self-condensation product of the amidic fatty acids, (b) the reaction product of polymeric fat acids and a polyami-ne of the formula H N(RNH) l-I where R is an alkylene radical having from 1 to 4 carbon atoms and x is an integer from 1 to 6, and (c) the reaction product of a polyamine of the formula H N(RNH) H where R is selected from the group consisting of arylene and alkylene radicals and z is an integer from 1 to 8 with a fatty acid derivative se-. lected from the group consisting of the epoxidized fatty acids and the alkyl esters thereof.

The first group of low melting point polyamides may be prepared by the self-condensation of an amidic fatty acid by heating an amidic fatty acid to provide a volatile organic acid and a residual linear polyamide. The amide substituted fatty acids are utilized directly in the preparation of this type of polyarnide.

These amidic fatty acids may be prepared in accord- 3,098,856 Patented July 23, 1963 ice 2 ance with the teachings of Roe and Swern, J. Am. Chem. Soc. 75, 5479 (1953); ibid, 77, 5408 (1955). Illustrated inthe following formula is the preparation of formamidostearic acid by the addition of hydrogen cyanide to oleic acid:

In place of hydrogen cyanide in the above reaction it is also possible to use nitriles of the general formula RCN where R represents a lower aliphatic hydrocarbon radical such as methyl, ethyl, propyl, isopropyl butyl, vinyl having not more than 6 carbon atoms.

Suitable acids which may be employed in addition to oleic acid include palmitoleic elaidic, linoleic and ricinoleic. It will be noted that these unsaturated acids occur in nature generally in the form of triglycerides, otherwise referred to as fats and oils. illustrative sources of these acids are the vegetable oils, cottonseed oil, soybean oil, "castor oil, tung oil and other similar oils, and the "animal and fish oils such as tallow and greases or tall oil.

The second group of low melting polyarnides which may beemployed are those prepared from the reaction of epoxidized fatty acids or esters and polyarnine compounds. The fatty acids which may be epoxidized are in general the fatty acids previously mentioned above.

The epoxidized fatty acid esters and fatty acids employed may be prepared by any of the well known methods. One method is to react any of the various ims'aturated fatty acids with peracetic acid at about room temperature. The peracetic acid may be preformed be fore the epoxidation step or formed in situ by any of the well known processes involving sulfonic acid resins utilizing hydrogen peroxide and acetic acid. Epoxidation can also be performed by the use of formic acid and hydrogen peroxide or by the addition of hypochlorous acid to the carbon-carbon double bond followed by dehydrochlorination.

illlustrative of the polyamine compounds are hydrazine, substituted hydrazines, and aromatic and aliphatic diarnines or polyamines which have the general formula H N(RNH) H where R is an arylene or alkylene radical and z is an integer from 1 to 8. The preferred class of polyarnine compounds are the ethylene linked aliphatic polyamines. Irnidazoline groups may be formed during the-polyamide reaction when the ethylene polyamines are employed.

It is possible to carry out the polyamide formation reaction in several ways. One preferred method is to carry out the reaction at about 150 C.at which temperature the ethylene polyamines react to form both imidazolines and amide linkages. Another method is to carry out the reaction atabout C. in which case the formation of amide linkages are favored, or at 200 C and above at which temperatures imidazoline linkages are favored. In any case the reaction temperature should not exceed 300 C. since deleterious side effects will occur above this temperature.

The third group of low melting point polyamides are those prepared from the polymeric fat acids and the alkylene d-iamines or polyamines having the formula H N-(R'NH) H Where R is an alkylene radical having from 1 to 4 carbon atoms and x is an integer from 1 to 6. The amidification reaction may be carried out under the usual conditions employed for this purpose. Generally this involves reaction at about 200 C. for approximately 3 hours.

The polymeric fat acids which are employed are those resulting from the polymerization of drying or semidrying oils, the free acids or the simple aliphatic alcohol ester-s thereof, for example, sources rich in linoleic acid. Suitable drying or semi-drying oils include soybean, linseed, tung, perilla, cottonseed, safflower, and dehydrated castor oil. Suitable fatty acids may also be obtained from tall oil, soap stock and other similar materials. In the polymerization process for the production of a polymeric fat acid, the fatty acids with suflicient double bond functionality combine for the most part, probably by a Diels-Alder mechanism, to provide a mixture of dibasic and higher polymeric fat acids. In place of this method of polymerization any other method of polymerization may be employed whether the resultant polymer possesses residual unsaturation or not. The term polymeric fat acid as used herein is intended to include the polymerized mixture of acids which usually contain a predominant portion of dimer acids, a small quantity of trimer and higher polymeric fat acids and some residual monomer.

Polymeric fat acids are readily available commercial products. Commercially these polymeric fat acids are best prepared from fatty acid mixtures that contain a. preponderance of linoleic acids since the only naturally occurring polyunsaturated acid available in large quantities is linoleic acid.

In addition it is understood that each of the groups of polyamides discussed above may be further modified with ordinary fatty acids, dibasic carboxyl-ic acids containing less than 14 carbon atoms and other reactants commonly employed in the preparation of polyam-ines.

The polyamides described above were then subjected to ionizing radiation. The irradiation was carried out in a concrete-lined well provided with water shielding using Co as a source of radiation as described by D. Young and L. F. Borchardt, Process Thru Research, vol. 10, No. l, 1956, pages 1-4 and 14. In general, the source holders maintain vertical capsules or pencils of 'Co in a circular arrangement so that samples can be lowered through a stainless steel pipe to a point located in the center of the circular arrangement of Co pencils at the bottom of the pool.

Example I Dosage M.P., Rex Peel Test degrees Hardness Megarads 100 Megarads. 111 68 Megarads 245 80 Megarads The peel test is carried out in a Thwing-Albert tensile tester in which two metal pieces such as tin plate are bonded together with the polyamide and each pulled in opposite directions (180) in the tester at a rate of one inch per minute. The table clearly illustrates the increase in melting point, hardness and peel strength caused by exposure to radiation.

Example II Dosage M.P., C. Rex

Hardness 30 Megarads (air) 226 95 30 Megarads (vacuum) 203 95 In this instance there is an increase in melting point while no adverse effect occurred in the hardness.

Example III Another sample of acetamidostearic acid polyamide but of lower melting point (72.5) was irradiated in the brass melting point ring in the same manner as described in Example I. The results are shown below:

Dosage I M.P., C. Hardness 2O Megarads.-. 40 Megarads Megareds Example IV A sample of polyamide prepared from 87 parts of polymeric fatty acids and 13 parts of monomeric fatty acids was heated to 185 F. and 11.2 parts of 93% ethylene diamine was added. The mixture was agitated for 2 hours at 230 F. Vacuum was then applied and the temperature was raised to 400 F. and held for 3 hours. The pnoduct, having a melting point of 106 C., was irradiated with large dosages from a C0 source,

Example V About 6 to 7 grams of a liquid polyamide prepared from the reaction at 300 C. for 2 hours of 300 grams of the methyl esters of epoxidized tall oil fatty acids and 146 grams of triethylene tetramine were sealed under water aspirator vacuum in each of 5, 25 of 200 mm. test tubes. These were irradiated with 0, 25, 40, 80, and 160 megarads of C0 gamma radiation. The samples became more viscous with increasing radiation, thus indicating that cross linking occurred.

The above examples clearly illustrate that cross linking was accomplished by ionizing radiation. This is shown by the increase in melting point. The original melting points of these type polyamides particularly of the variety derived from C fatty acids ordinarily reach an upper limit of about C. with increasing molecular size. However, after exposure to gamma radiation this melting point can be raised to 260 C. or more. This raise in melting point was achieved without any adverse aflFect on the hardness which in many instances also increased. This radiated product also showed an increase in peel strength.

The above examples show that increased cross linking occurs with increased dosage. In Example I as little as megarads dosage produced an increase in melting point. Dosages up to 160 megarads were used and great increases in melting point Were observed. In Example V, viscosity increased with increasing radiation indicating cross linking occurred. With higher dosage gellation would occur.

Many modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope of, and therefore only such limitations should be imposed as are indicated in the appended claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

l. A method of cross linking a fatty acid polyamide having a melting point below 130 C., said fatty acid polyamide being selected from the group consisting of (a) the self condensation product of amidic fatty acids, (b) a polyamide derived from the reaction of polymeric fat acids and a polyamine of the fiormula H N(RNH) H where R is an alkylene radical having from 1 to 4 carbon atoms and x is an integer from 1 to 6, and (c) a polyamide derived from the reaction of a polyamine of the formula H N(RNI-I) H where R is selected from the group consisting of arylene and alkylene radicals and z is an integer from 1 to 8 and a fatty acid derivative selected from .the gnoup consisting of the epoxidized fatty acids and the alkyl esters thereof, comprising subjecting said fatty acid polyamide to high energy ionizing radiation in a dosage of from 10 to megarads.

2. A method as defined in claim 1 wherein said amidic fatty acid is acetamidostearic acid.

3. A method of cross linking as wherein R is ethylene and x is 1.

4. A method of cross linking a fatty acid polyamide as defined in claim 1 wherein R is an ethylene radical.

5. The irradiated product of claim 1.

defined in claim 1 References Cited in the file of this patent UNITED STATES PATENTS (3rd addition to No. 1,079,401) OTHER REFERENCES Bopp et al.: Nucleonics, volume 13 (July 1955). 

1. A METHOD OF CROSS LINKING A FATTY ACID POLYAMIDE HAVING A MELTING POINT BELOW 130*C., SAID FATTY ACID POLYAMIDE BEING SELECTED FROM THE GROUP CONSISTING OF (A) THE SELF CONDENSATION PRODUCT OF AMIDIC FATTY ACIDS, (B) A POLYAMIDE DERIVED FROM THE REACTION OF POLYMERIC FAT ACIDS AND A POLYMINE OF THE FORMULA H2N(R''NH)XH WHERE R'' IS AN ALKYLENE RADICAL HAVING FROM 1 TO 4 CARBON ATOMS AND X IS AN INTEGER FROM 1 TO 6, AND (C) A POLYAMIDE DERIVED FROM THE REACTION OF A POLYAMINE OF THE FORMULA H2N(RNH)ZH WHERE R IS SELECTED FROM THE GROUP CONSISTING OF ARYLENE AND ALKYLENE RADICALS AND Z IA N INTEGER FROM 1 TO 8 AND A FATTY ACID DERIVATIVE SELECTED FROM THE GROUP CONSISTING OF THE EPOXIDIZED FATTY ACIDS AND THE ALKYL ESTERS THEREOF, COMPRISING SUBJECTING SAID FATTY ACID POLYAMIDE TO HIGH ENERGY IONIZING RADIATION IN A DOSAGE OF FROM 10 TO 160 MEGARADS. 